5G E1AP Messages – Complete CU-CP and CU-UP Message List

E1AP, or E1 Application Protocol, is the control-plane protocol used on the E1 interface between the gNB-CU-CP and gNB-CU-UP in a split 5G RAN architecture. Defined in 3GPP TS 38.463, E1AP supports E1 interface setup, gNB-CU-UP configuration, bearer context setup, modification and release, inactivity notification, data usage reporting, reset, and error handling between the control-plane and user-plane parts of the gNB-CU.

Use this page to search or browse 5G E1AP messages by procedure category. Each message page explains the message direction, trigger, call-flow role, key Information Elements, and practical troubleshooting notes.

Based on 3GPP TS 38.463

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E1 Interface Management Messages

Non-UE-associated procedures used to establish, reset, update, and manage the E1 interface between gNB-CU-CP and gNB-CU-UP.

6 messages

gNB-CU-UP -> gNB-CU-CP

E1 Setup Request

Starts E1 interface setup and advertises CU-UP identity and capabilities.

Coming soon

gNB-CU-CP -> gNB-CU-UP

E1 Setup Response

Accepts E1 setup and returns CU-CP-side setup context.

Coming soon

gNB-CU-CP -> gNB-CU-UP

E1 Setup Failure

Rejects E1 setup with cause and retry context.

Coming soon

gNB-CU-CP <-> gNB-CU-UP

E1 Reset

Requests reset of E1 interface or bearer contexts.

Coming soon

gNB-CU-CP <-> gNB-CU-UP

E1 Reset Acknowledge

Confirms completion of requested E1 reset handling.

Coming soon

gNB-CU-CP <-> gNB-CU-UP

Error Indication

Reports E1AP protocol errors or invalid procedure handling.

Coming soon

gNB-CU-UP Configuration Messages

Messages used to update or acknowledge gNB-CU-UP configuration and capacity/overload information.

3 messages

gNB-CU-UP -> gNB-CU-CP

gNB-CU-UP Configuration Update

Updates CU-UP configuration, capacity, support, or overload-related information.

Coming soon

gNB-CU-CP -> gNB-CU-UP

gNB-CU-UP Configuration Update Acknowledge

Confirms successful CU-UP configuration update processing.

Coming soon

gNB-CU-CP -> gNB-CU-UP

gNB-CU-UP Configuration Update Failure

Rejects CU-UP configuration update with cause.

Coming soon

Bearer Context Setup Messages

UE-associated procedures used by the gNB-CU-CP to create bearer context resources at the gNB-CU-UP.

3 messages

gNB-CU-CP -> gNB-CU-UP

Bearer Context Setup Request

Requests CU-UP bearer context creation for UE user-plane resources.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Setup Response

Reports successful bearer context setup and user-plane resource allocation.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Setup Failure

Reports failed bearer context setup with cause.

Bearer Context Modification Messages

Messages used to modify existing bearer contexts, PDU session resources, DRBs, QoS flow mappings, UP parameters, and user-plane tunnel information.

5 messages

gNB-CU-CP -> gNB-CU-UP

Bearer Context Modification Request

Requests modification of bearer context, DRB, QoS, tunnel, or PDU session resources.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Modification Response

Reports successful bearer context modification.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Modification Failure

Reports failed bearer context modification.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Modification Required

Requests CU-CP action for CU-UP-initiated bearer context modification.

gNB-CU-CP -> gNB-CU-UP

Bearer Context Modification Confirm

Confirms CU-UP-initiated bearer context modification handling.

Bearer Context Release Messages

Messages used to release bearer context resources between gNB-CU-CP and gNB-CU-UP.

3 messages

gNB-CU-CP -> gNB-CU-UP

Bearer Context Release Command

Commands release of bearer context resources in the CU-UP.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Release Complete

Confirms bearer context release completion.

gNB-CU-UP -> gNB-CU-CP

Bearer Context Release Request

Requests bearer context release from the CU-UP side.

Bearer Context Status / Inactivity Messages

Messages used by the CU-UP to notify the CU-CP about bearer activity, inactivity, and uplink data availability.

2 messages

gNB-CU-UP -> gNB-CU-CP

Bearer Context Inactivity Notification

Notifies CU-CP about bearer inactivity status.

Coming soon

gNB-CU-UP -> gNB-CU-CP

UL Data Notification

Notifies CU-CP that uplink data is available for a bearer context.

Coming soon

Data Usage Reporting Messages

Messages used to report data usage information for PDU sessions, DRBs, or usage-related accounting.

1 messages

gNB-CU-UP -> gNB-CU-CP

Data Usage Report

Reports usage information for PDU sessions, DRBs, or accounting-related handling.

Coming soon

Reset & Error Handling Messages

Messages used to reset E1 contexts or report protocol-level errors.

3 messages

gNB-CU-CP <-> gNB-CU-UP

E1 Reset

Requests reset of E1 interface or bearer contexts.

Coming soon

gNB-CU-CP <-> gNB-CU-UP

E1 Reset Acknowledge

Confirms completion of requested E1 reset handling.

Coming soon

gNB-CU-CP <-> gNB-CU-UP

Error Indication

Reports E1AP protocol errors or invalid procedure handling.

Coming soon

Advanced / Release-Specific Messages

Additional E1AP messages used for release-specific features, redundancy, QoS, MBS, IAB, or advanced user-plane coordination.

0 messages

Most Used E1AP Messages

E1 Setup Request Coming soon

E1 Setup Response Coming soon

gNB-CU-UP Configuration Update Coming soon

Bearer Context Setup Request Requests CU-UP bearer context creation for UE user-plane resources. Bearer Context Setup Response Reports successful bearer context setup and user-plane resource allocation. Bearer Context Modification Request Requests modification of bearer context, DRB, QoS, tunnel, or PDU session resources. Bearer Context Modification Response Reports successful bearer context modification. Bearer Context Modification Required Requests CU-CP action for CU-UP-initiated bearer context modification. Bearer Context Modification Confirm Confirms CU-UP-initiated bearer context modification handling. Bearer Context Release Command Commands release of bearer context resources in the CU-UP. Bearer Context Release Complete Confirms bearer context release completion. Bearer Context Release Request Requests bearer context release from the CU-UP side.

Bearer Context Inactivity Notification Coming soon

UL Data Notification Coming soon

Common E1AP Procedure Flows

E1 Setup Flow

E1 Setup Request -> E1 Setup Response / E1 Setup Failure

gNB-CU-UP Configuration Update Flow

gNB-CU-UP Configuration Update -> Acknowledge / Failure

Bearer Context Setup Flow

Bearer Context Setup Request -> Bearer Context Setup Response / Failure

Bearer Context Modification Flow

Bearer Context Modification Request -> Bearer Context Modification Response / Failure

CU-UP Initiated Bearer Context Modification Flow

Bearer Context Modification Required -> Bearer Context Modification Confirm

Bearer Context Release Flow

Bearer Context Release Command -> Bearer Context Release Complete

CU-UP Initiated Bearer Context Release Flow

Bearer Context Release Request -> Bearer Context Release Command -> Bearer Context Release Complete

Inactivity / UL Data Flow

Bearer Context Inactivity Notification; UL Data Notification

FAQ

What is E1AP in 5G?

E1AP is the E1 Application Protocol used between gNB-CU-CP and gNB-CU-UP.

Which interface uses E1AP?

E1AP is used on the E1 interface between the control-plane and user-plane parts of the gNB-CU.

Which 3GPP specification defines E1AP?

E1AP is defined in 3GPP TS 38.463.

What is the difference between E1AP and F1AP?

F1AP runs between gNB-CU and gNB-DU, while E1AP runs between gNB-CU-CP and gNB-CU-UP.

What is the difference between E1AP and NGAP?

NGAP runs between NG-RAN and AMF over N2, while E1AP is internal to the split gNB-CU architecture.

What are the most important E1AP messages?

Important E1AP messages include E1 Setup, Bearer Context Setup, Modification, Release, Inactivity Notification, UL Data Notification, Reset, and Error Indication messages.

What is Bearer Context in E1AP?

Bearer Context procedures create, modify, and release user-plane bearer resources in the gNB-CU-UP.

How does E1AP relate to gNB-CU-CP and gNB-CU-UP?

E1AP lets the gNB-CU-CP control user-plane resources in the gNB-CU-UP while keeping control-plane and user-plane functions separated.

References

3GPP TS 38.463 – NG-RAN; E1 Application Protocol (E1AP)
3GPP TS 38.401 – NG-RAN architecture description
3GPP TS 38.460 – E1 general aspects and principles
3GPP TS 38.461 – E1 interface layer 1
3GPP TS 38.462 – E1 signalling transport